An experimental study on WGS catalysts: Relating performance under realistic feel with oxygen holding capacity

Abstract

The present work is a part of an ongoing study aiming to design and develop high performance, steam tolerant, non-pyrophoric WGS catalyst(s) to be used in a demo-scale fuel processor (DFP) producing PEM grade hydrogen for PEM fuel cells. The current work mainly focuses on developing a reliable methodology for determination of oxygen storage capacity (OSC) of the catalysts through the use of operando IGA-MS analysis; and establishing a relation between WGS activity and OSC. In this context, Pt-Re-V/CeO2 catalysts were prepared, characterized and tested in WGS performance tests for two realistic feed compositions at 300, 350, 400 and 450 °C for fixed GHSV at 120,000 ml gcat-1 h-1. The freshly reduced and spent samples were characterized by SEM, XPS, Raman spectroscopy and CO Chemisorption. The results of the catalytic tests indicated that 1Pt-1Re-1V sample having superior performance may be a great candidate to be used in a fuel processor with its high activity, selectivity and stability. The OSC values of the samples were determined through a novel operando IGA-MS methodology under two realistic feed compositions at 350 °C by fixed GHSV as 40,000 ml gcat-1 h-1. Additional OSC tests were also conducted at 400 and 450 °C over the sample having superior performance. The combined evaluation of WGS performance and operando OSC results point out that; there are two types of OSCs, structural (S-OSC) and effective (E-OSC), having prominent effect on WGS performance; increasing reaction temperature was found to have a negative effect on E-OSC; and the surface groups determined in S-OSC measurements have significant roles, especially at the time when reactive mixture first contacts the catalyst, in water activation, while, after surface concentrations and redox mechanism reach steady state, E-OSC becomes the primary factor affecting WGS activity.